Multiple-beam klystron apparatus with waveguide periodically loaded with resonant elements



Oct. 11, 1966 T. MIHRAN 3,

MULTIPLE-BEAM KLYSTRON APPARATUS WITH WAVEGUIDE PERIODICALLY LOADED WITH RESONANT ELEMENTS Filed Dec. 5, 1962 2 Sheets-Sheet 1 Fig,

HEW TEE SUPPLY in verv'bor-n' Theodor-e GM/hrdn,

T. G. MIHRAN Oct. 11, 1966 3,278,795 MULTIPLE-BEAM KLYSTRON APPARATUS WITH WAVEGUIDE PERIODICALLY LOADED WITH RESONANT ELEMENTS 5, 1962 2 Sheets-Sheet 2 Filed Dec.

u AllilILlll 0 & uwa 09mm 1'1 3 7 FHA SE SH/FT PER SE07! ON SECOND PASS BAA/0 S 7UP BAND FIRST PASS [7) vervror: Theodor-e G. M/hr-dn, Attor-me I l *22 2 PHASE SHIFT PER SECT/O/V' United States Patent MULTIPLE-BEAM KLYSTRON APPARATUS WITH WAVEGUIDE PERIODICALLY LOADED WITH RESONANT ELEMENTS Theodore G. Mihran, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Dec. 3, 1962, Ser. No. 241,855 6 Claims. (Cl. 315-5.14)

This invention relates to new and improved multiplebeam radio frequency apparatus capable of generating and handling relatively high electromagnetic wave power at relatively high frequencies.

In copending US. appln. S.N. 173,724 of M. R. Boyd et al. filed February 16, 1962, now Patent No. 3,248,597, and assigned to the same assignee as the present inven tion, there is disclosed and claimed multiple-beam radio frequency apparatus which is particularly adapted for generating and handling substantially high electromagnetic wave power at microwave frequencies and in a manner effective for minimizing mode interference problems of the type theretofore encountered in multiple-beam devices. Also, the mentioned apparatus is adapted for generating and handling power levels equivalent to the total power of a plurality of individual single-beam radio frequency power generating devices which capability had not been accomplished with prior multiple-beam devices.

The above-mentioned Boyd et al. apparatus is adapted for affording maximum mode separation and low attenuation when operating in a 'n'/ 2 mode. The present invention contemplates multiple-beam apparatus wherein each electron beam is adapted for being acted upon by the full radio frequency voltage and yet is in the middle of a propagating region where maximum mode separation and low attenuation is still obtained. In other words, the present apparatus is adapted for affording desired maximum mode separation and low attenuation when operating normally in a 11' mode.

It is, accordingly, an object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for generating and handling substantially high electromagnetic wave power at microwave frequencies.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for operation in a 1|- mode with maximum mode separation and low attenuation.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus for generating and handling large amounts of electromagnetic wave power at microwave frequency ranges and in such a manner that mode interference problems do not severely restrict .the number of electron beams employed in the power genera-tion.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for generating and handling large amounts of electromagnetic wave power at microwave frequencies equivalent to the total power of a plurality of individual single-beam radio frequency power generating devices.

It is another object of this invention to provide new and improved multiple-beam radio frequency apparatus adapted for relatively low voltage operation in the generation of large amounts of electromagnetic wave power of microwave frequencies and thereby adapted for minimizing problems regarding voltage breakdown and power supply and X-ray radiation shielding requirements in the operation of such apparatus.

3,278,795 Patented Oct. 11, 1966 "ice Further objects and advantages of this invention will become apparent as the following description proceeds and the features of novelty which characterize this in= vention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of this invention, and according to one embodiment thereof, there is provided multiple-beam radio frequency apparatus comprising input, output, and preferbaly at least on intermediate, longitudinally-resonant sections of transmission line preferably in the form of longitudinally resonant waveguides. The resonant waveguides are supported in spaced parallel relation; and extending perpendicular to and in operative association with the waveguides are at least several parallel klystron-like beam devices. Each of such devices includes a plurality of axially spaced drift tubes interconnecting respective ones of the mentioned waveguides, an electron gun for projecting a beam of electrons through the drift tubes and waveguides and a collector for collecting the electrons emerging from the last drift tube. In each waveguide each beam cooperates with a resonant element located in the plane of the beam. The resonant elements can comprise capacitive interaction gaps defined by reentrant portions of the drift tube sections and electrically cooperating inductive irises located in the planes of the interact-ion gaps. Alternatively, the resonant elements can comprise resonant helix sections each having a beam extending axially therethrough. The resonant elements in each waveguide are equally spaced apart one half of a waveguide wavelength and the end resonant elements are spaced one quarter of a waveguide wavelength from the end walls of the waveguides at a predetermined operating frequency. Thus, each resonant waveguide constitutes a periodically-loaded, longitudinally-resonant section of transmission line with the periodic loading resulting from the provision therein of the equally-spaced resonant elements. Sui-table means, such as an inductive coupling loop, is provided for exciting the input waveguide to establish therein a standing electromagnetic wave of the aforemention predetermined frequency which results in the occurrence of an electric field maximum at each resonant element in the input waveguide. Thus, 1r radians of phase shift exist between each adjacent pair of recurring resonant elements and 11/2 between the end resonant elements and the end walls, and the apparatus is caused to operate in its 7r mode. The standing electromagnetic wave thusly excited in the input waveguide velocity modulates all of the electron beams and each of the beams becomes density modulated in a subsequent field-free drift region. The density modulated beams cooperatively excite similar standing waves in the intermediate waveguides which results in further density modulation of the beams in subsequent drift regions. Finally, the density modulated beams cooperatively induce a co-rresponding amplified standing electromagnetic wave in the output waveguide. In the output waveguide also the electric field maxima occur at the resonant elements. The electromagnetic wave energy is extracted from the output waveguide by any suitable means, such as an inductive coupling loop or an inductive output iris.

For a better understanding of the invention, reference may be had to the accompanying drawing in which;

FIGURE-1 is a sectional view of a multiple-beam electron discharge device constructed according to one embodiment of the invention and incorporating four electron-beam-producing means;

FIGURE 2 is a cross-sectional view taken along the stepped line 22 in FIGURE 1 and looking in the direction of the arrows;

FIGURE 3 is a broken-away, fragmentary, perspective view illustrating the resonant elements of FIGURES 1 and 2;

FIGURE 4 is an w-fl diagram showing the usual graphical relation between the frequency of operation of a capacitively, periodically-loaded waveguide and the phase shift per section of such a waveguide;

FIGURE 5 is an w-fi diagram showing the graphical relation between the frequency of operation of a Waveguide periodically loaded according to the present invention and the phase shift per section of such a waveguide; FIGURE 6 is a broken-away, fragmentary, perspective view illustrating a modified form of the present invention; and

FIGURE 7 is a broken-away, fragmentary, perspective view illustrating another modified form of the present invention.

Referring now to FIGURE 1, there is shown multiplebeam radio frequency amplifying apparatus constructed in accordance with the invention. More specifically, the arrangement of FIGURE 1 is an electron discharge device in which D.C. energy from four electron beams is converted into electromagnetic wave energy and which has substantially four times thepower generating and handling capabilities of a conventional klystron utilizing a single beam of comparable dimensions. However, from the outset, it is to be understood that this invention is not limited to a device having four beams. Instead, the invention can be used in providing devices having almost any number of electron beams, the limit depending only on the impedance per beam and the fact that at some substantially large number of beams the mode separation will be so small as to make the construction of a practical operative device ditficult.

The device of FIGURE 1 is constructed as a unitary evacuated envelope comprising four resonant waveguides designated 1-4 arranged in spaced parallel relation and a plurality of transversely-extending, equally-spaced cooperating klystron-like beam devices designated 5-8. In this arrangement each of the waveguides 1-4 is a shortcircuited, or longitudinally-resonant, section of a periodically-loaded waveguide, the specific structure and func-, tion of which will be discussed in detail hereinafter. The waveguides can have a rectangular cross-section as illustrated in FIGURES 1-3 or can be of any desired crosssectional configuration. Also, the waveguides each include conductive end walls which serve to short electrically the ends thereof and to maintain a suitable vacuum in the assembly. Further, each waveguide is provided with a suitable tuning means which, as shown, can comprise sliding end-wall tuners 9 of a type well known in the art.

The lowermost waveguide 1 in FIGURE 1 constitutes an input resonator and is adapted to be excited for having a standing electromagnetic wave established therein by any suitable radio frequency input-coupling means such as an inductive loop 10 shown in FIGURES 2 and 3. The input resonator is effectively employed to velocity modulate the beams of the devices 58. The uppermost waveguide 4 in FIGURE 1 constitutes an output resonator and is adapted for having an amplified electromagnetic wave induced therein. Energy is extracted from the output resonator by any suitable radio frequency output means, such as an inductive loop 11 shown in FIGURE 1; Interposed between the input and output resonators 1 and 4 areintermediate resonators 2 and 3, which are shown as two in number but which can be employed in any desired number. These resonators serve to increase power modulation and bunching efliciency in generally the same well-known manner as intermediate resonators found in the klystron art.

The beam devices 58 each comprise a gun section 12 reentrantly in one side of the input resonator 1 and an emitter generally designated 14 adapted for directing a beam of electrons axially through the section 13. Axially aligned with each section 13 and interconnecting the several resonators are a plurality of drift tubes 15, and axially aligned therewith andextending from the output resonator 4 is a tubular section 16 connected to a collector 17. Surrounding the described assembly is a solenoid coil 18 providing a collimating magnetic field extending parallel to the axes of the beam devices and adapted for focusing the several electron beams therein. The entire assembly is enclosed by a casing 19 formed, for example, of a material of low reluctance, such as soft iron, to provide uniformity of the axial magnetic field in the region through which the electron beams pass. The electron guns 12, which can be located outside the casing in the manner shown, are supplied with operating potentials from any suitable sources indicated by the legends Anode Power Supply and Heater Supply and which are well known to those skilled in the art.

In the described arrangement the tubular sections 13 and 16 and drift tubes 15 extend reentrantly in the several waveguides to define therein reentrant active capacitive gaps 20 which have uniform capacitance values across each waveguide. As best seen in FIGURES 2 and 3 the gaps 20 each cooperate with an inductive iris defined by a pair of spaced vertical conductive septa 21 straddling, or lying on opposite sides of, an associated gap 20 and located in a plane extending perpendicular to the longitudinal axis of the waveguide and through the longitudinal axis of the associated gap. The thickness of each septum 21 is small in comparison with the waveguide wavelength of an electromagnetic wave within the waveguide. Additionally, each iris is of an appropriate inductance value to cooperate with its associated capacity gap 20 to define a resonant element. More specifically, the magnitude of the inductive reactance introduced into the waveguide circuits by each iris is preferably made equal to the magnitude of the capacitive reactance introduced by its associated capacity gap 20 at the predetermined operating frequency which determines the spacing between the gap-defining reentrant sections. Thus, at this frequency the capacitive effects of the gaps are resonated out by the inductive irises. Also, the spacing between each adjacent pair of resonant elements is equal to one half of a waveguide wavelength and the spacing between each endmost resonant element and the adjacent waveguide end wall is equal to one quarter of a waveguide wavelength at the mentioned predetermined operating frequency. While the arrangement of FIGURES 13 employs a pair of septa 21 defining each iris, it is to be understood from the foregoing that a single septum 21 of suitable dimension to afford the necessary inductance at each gap location for effecting the desired resonance is equally employable.

The operation of the above-described multiple-beam device is as follows: A standing electromagnetic wave is established in the input resonator 1 by R.F. energy introduced thereinto through the input coupling loop 10. This wave has electric field maxima occurring at each of the active gaps 20. Theactive gaps 20 comprise interaction gaps and the electrons in each of the electron beams passing through these gaps become velocity modulated in the gaps in a manner well known to those skilled in the klystron art. After passing through the drift tubes 15 for a suitable predetermined distance, the electron beams become density modulated in accordance with the input signals to the input resonator 1, again in a manner well known to those skilled in the klystron art. The densitymodulated electron beams, or bunches in the beams, pass successively through the gaps 20 in the intermediate resonators and the drift spaces 15 which results in greater density modulation. Thereafter, the 'beams traverse the gaps 20 of the output resonator 4 and cooperatively induce therein an amplified standing electromagnetic wave corresponding in form to the standing electromagnetic wave established in the input resonator 1 in a manner similar to that which is well known in the klystron art. The electromagnetic wave induced in the output resonator 4 thus has electric field maxima occurring at each of the active gaps 20. This electromagnetic wave energy can be extracted through the output coupling loop 11 and a coaxial line. The electrons constituting the beams are then collected in the electron collectors 17.

The operation of the device and the advantages of the present invention will be better understood from a discussion of the propagation and wave-supporting characteristics of the periodically-loaded waveguides provided in the above-described structure. An electromagnetic wave in either of the resonators 14 is presented with periodically arranged impedances in the forms of the active capacitive gaps 20 and the inductive irises defined by the septa 21. Thus, each of the resonators 1-4 is, in effect, an electrically short-circuited section of a periodically-loaded waveguide with the periodic loading afforded by resonant elements each comprising a capacitive gap and cooperating inductive iris.

FIGURE 4 is an w-fi diagram and shows the graphical relation of the phase shift per section of matched periodically loaded waveguides as -a function of the frequency of an electromagnetic wave within such waveguides; and wherein the periodic discontinuities are simple singlyreactive elements such as either capacitive posts or inductive irises. Such a periodically loaded waveguide, as in an unloaded waveguide, has a lower limit of frequency, or lower cut-off frequency, below which energy cannot be propagated therethrough. In general, the group velocity is proportional to the slope of the w-B diagram. Thus, at the lower frequency edge where the slope approaches 0 the group velocity approaches 0 and thus the guide wavelength approaches infinity. As frequency increases above the lower cut-off frequency, propagation becomes possible; the wavelength along the guide is diminished and the group velocity is increased from 0. If

the frequency is continuously increased above the lower cut-off, a frequency will ultimately be reached where the spacing between adjacent reoccurring loads in the periodically loaded waveguide becomes equal to one half a Waveguide wavelength. At this frequency the phase shift between adjacent impedances is equal to 1r radians. The reflection from an impedance then reinforces the reflection from the immediately-preceding impedance and the overall effect in a long waveguide is total reflection and no propagation. Thus, at this frequency the group vel0city is again 0 as is the slope of the w-B diagram, and this frequency may be referred to as an upper cut-oft frequency. A matched periodically-loaded waveguide serves as a band-pass filter for frequencies between these upper and lower cut-off frequencies and the range between these frequencies may be termed the first pass band of the band pass filter.

For a range of frequencies immediately above the first cut-off frequency, the periodically-loaded waveguide will not propagate electromagnetic wave energy and therefore a stop band exists over these frequencies. However, at a higher frequency, which may be termed the second lower cut-off frequency, propagation again becomes possible and a second pass band exists over a frequency range similar to that of the first pass band, with the phase shift between adjacent periodic impedances varying from 1r radians per section for the lower cut-off frequency to 271' radians per section at the second cut-off frequency. This range of frequencies defines a second pass band for the periodically-loaded waveguide. quency edge of the second pass band the slope of the w-fl diagram is 0, as it is in the case of the first pass band. A periodically loaded waveguide also has other pass bands and stop bands at higher frequencies, but they are of no interest for the present discussion.

While the matched periodically-loaded waveguide may support an electromagnetic wave having a frequency of Again, at the lower freany value within a pass band, an additional limitation exists when a periodically-loaded waveguide is made resonant by terminating the ends in short circuits. Resonance occurs in a shortcircuited, periodically-loaded waveguide only at those frequencies in which the structure is an integral number of guide half wavelengths long. In a short-circuited, periodically-loaded waveguide the total phase shift along the guide must thus be an integral multiple of 11'. In other words, resonance occurs only at the discrete frequencies at which the difference in phase of the wave at two adjacent impedances is 1rn-/N where N is the number of sections into which the line is divided by the periodic imepdances and n is any integer from 1 to N.

In the described type of device maximum energy transfer between an electromagnetic wave in one of the waveguides and an electron 'beam occurs when the electron beam sees an optimum electric field when traversing an interaction gap 20. If each of the waveguides 1-4 consisted of a short-circuited section of matched periodically-loaded waveguide in which the periodic loading consisted of only capacitive gaps, and the inductive irises 7 of the invention were omitted, the waveguides could be excited so as to support a standing electromagnetic wave which has an electric field maxima occurring at each of the capacitive gaps. This arrangement would satisfy the requirement that each electron beam see an optimum electric field at the point of interaction. However, 1r radians of phase shift occur between each of the adjacent impedance devices and a reference to FIGURE 4 shows that, under these conditions, a periodically loaded waveguide is operated at the upper cut-off frequency of the first pass band. It is further observed that in this region of the 10-5 diagram, the frequency separation between adjacent modes at which operation is possible is at a minimum, due to the fiat slope of the characteristic curve, and therefore adjacent mode interference is a serious problem.

FIGURE 5 shows the w-B diagram for a matched periodically-loaded section of waveguide of the type incorporated in the present invention and wherein the periodic discontinuities consist of resonant elements consisting of the capacitive gaps 20 and the associated inductive irises defined by the septa 21. It is observed from FIGURE 5 that such a matched periodically loaded waveguide also has a lower cut-off frequency, at which the slope of the w-,@ diagram is 0 and that, as the frequency increases above this value, the slope of the wdiagram increases until a phase shift per section of 1r radians is obtained, at which point the slope of the diagram is a maximum. As the frequency is increased above this value, the slope of the w-B diagram again decreases, until the frequency is reached at which a phase shift per section of 21r radians is attained, at which point the slope of the 01-5 diagram is again 0, with this frequency being the upper cut-olf frequency of this pass band of such a matched periodically-loaded waveguide. Thus, when the waveguide is periodically loaded with resonant elements in accordance with the present invention, the first and second pass bands of a periodicallyloaded waveguide having singly reactive periodic discontinuities are, in effect, merged into a single pass band. Also, inasmuch as the slope of the w-fi diagram of FIG- URE 5 is a maximum at the frequency corresponding to 11' radians of phase shift per section, which is to say in the 11' mode, which mode provides the maximum mode separation for the periodically-loaded waveguide. Thus, when the device of FIGURES 1-3 is excited with a standing electromagnetic wave in which an electric field maxima occurs at each of the capacitive gaps 20 therein, the device is operating in its 1r mode and is adapted for maximum adjacent mode separation. Additionally, this manner of operation is obtained without introducing undesired attenuation.

FIGURE 6 shows a view of one of the resonators 1-4 of FIGURE 1 incorporating a modified form of resonant element. In this figure there is shown a resonator 1 having capacity gaps 20 defined by reentrant portions of drift tubes and which can be spaced one half of a waveguide wavelength apart for the mentioned predetermined operating frequency. In accordance with this embodiment of the invention, an iris is provided in the trans verse plane of each gap 20; however, these irises are both inductive and capacitive and take the form of apertured members 22 having a thickness equal to the diameter of the reentrant tubular portions which define the gaps 20. The members 22 constitute constrictions built up around the walls of the resonator 1 at the point of the reentrant portions and are designed to resonate out the capacitive effects of the gaps as well as any capacitive effects introduced into the circuit by the irises.. At the resonant frequency, each resonant iris shunts a high impedance across the waveguide which causes very little reflection of power. Thus, electrically the irises would appear not to be present in the guides. The exact dimensions and shaping of the members 22 can be determined experimentally in a manner well known to those skilled in the waveguide art. Also, it is to be understood from the foregoing that the resonators 24 can be constructed to include the same resonant elements as illustrated in FIGURE 6.

FIGURE 7 illustrates a resonator embodying yet another form of the invention. Therein is shown a resonator 1 having inductive helices 23 interconnectingopposite walls of the waveguide section and positioned one half of a waveguide wavelength apart for the predetermined frequency. The electron beams are projected axially through the helices 23 and the interaction between the beams and helices takes place along the entire lengths of the helices. A pair of opposed conductive hemispherical sections, or end :bells, 24 surround and shield each end of each helix to assure a satisfactory coupling between the helix fields and the waveguide fields. This structure affords a higher R/ Q than the above-described resonant iris structure and thus is adapted for greater bandwidth operation. It is to be understood from the foregoing that the just-described periodic impedance structures can be incorporated in each of the waveguides 1-4. Additionally, the disclosed cooperation of an electron beam and a resonant helix having its opposed ends shielded by end bells does not constitute part of the presently claimed invention but is disclosed and claimed in copending US. appln. S.N. 159,004 of Norman T. Lavoo, filed December 13, 1961 and assigned to the same assignee as the present invention. The present invention involves the provision of a multiple-beam radio-frequency apparatus incorporating such resonant helices at predetermined locations in a resonant waveguide.

While the invention is thus shown and the mode of operation of several embodiments described, the invention is not limited to these shown embodiments. Instead, many modifications will be suggested from the foregoing to those skilled in the art and which will come within the spirit and scope of the invention. For example, the invention is not limited to use in a device using four electron beams, but may be used in a device having any desired number of electron beams. Also, the input and output waveguides need not necessarily take the shape of a straight section of waveguide, but can instead take the form of a curved section of waveguide if desired. It is thus intended that the invention be limited in scope only by the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A multiple beam klystron apparatus comprising spaced longitudinally resonant input and output waveguides, input means for establishing in said input waveguide a standing electromagnetic wave at a predetermined operating frequency, each said waveguides being periodically loaded by a longitudinally extending array of resonant elements equally spaced apart one half of a waveguide Wavelength and spaced from the ends of said sections one quarter of a waveguide wavelength at said predetermined operating frequency, means for projecting a plurality of discrete electron beams transversely across said waveguide in succession and coincident with said resonant elements for interaction therewith, means defining drift spaces between said waveguides for conversion of velocity modulation of said electron beams to density modulation, whereby an electromagnetic wave is introduced in said output waveguide corresponding in form to said wave in said input waveguide, and means for extracting radio frequency energy from said output waveguide.

2. Radio frequency apparatus comprising at least a pair of spaced longitudinally-resonant input and output waveguides, input means for establishing in said input waveguide a standing electromagnetic wave at a predetermined operating frequency, each said waveguides being periodically loaded by a longitudinal array of resonant elements equally spaced apart one half of a waveguide wavelength and spaced from the. ends of said waveguide one quarter of a waveguidewavelength at said predetermined operating frequency, said resonant elements each comprising an interaction gap and a coaxial cooperating inductive iris, means for projecting a plurality of discrete electron beams transversely across said gaps in succession, means defining drift spaces between said gaps for conversion of velocity modulation of said electron beams to a density modulation, whereby an electromagnetic wave is induced in said output waveguide corresponding in form to said wave in said input waveguide, and means for extracting radio frequency energy from said output waveguide.

3. Multiple beam klystron apparatus according to claim 2, wherein said interaction gaps are defined by cooperating oppositely extending reentrant portions in said waveguides and said inductive irises are defined by septa extending transverse in said waveguide in the planes of said a-ps.

4. Multiple beam klystron apparatus comprising at least a pair of spaced longitudinally-resonant input and output waveguides, input means for establishing in said waveguide a standing electromagnetic wave at a predetermined operating frequency, each of said waveguides being periodically loaded by a longitudinally extending array of apertured conductive elements extending transverse of said waveguides and equally spaced apart one half of a Waveguide wavelength and spaced from the ends of said waveguide one quarter of a waveguide wavelength at said predetermined operating frequency, said conductive elements each including tubular oppositely extending portions defining an interaction gap and interconnecting side portions defining inductances, means for projecting a plurality of discrete electron beams transversely across said gaps in succession, means defining drift spaces between said gaps for conversion of velocity modulation of said electron beams to density modulation, whereby an electromagnetic wave is induced in said outward waveguide corresponding in form to said wave in said input waveguide, and means for extracting radio frequency energy from said output waveguide.

5. Multiple beam klystron apparatus comprising at least a pair of spaced longitudinally-resonant input and output waveguides, input means for establishing in one of said waveguides a standing electromagnetic wave at a predetermined operating frequency, each said waveguides being periodically loaded by a longitudinally extending array of resonant helices equally spaced apart one half of a waveguide Wavelength and spaced from the ends of said waveguides one quarter of a waveguide wavelength at said predetermined operating frequency, said helices each conductively connecting the opposite walls of the respective waveguide, means for projecting a plurality of discrete electron beams transversely across said w aveguides and axially through said helices in succession, means defining drift spaces between said waveguides for conversion of velocity modulation of said electron beams to density modulation, whereby an electromagnetic wave is induced in said output waveguide corresponding in form to said wave in said input waveguide, and means for extracting radio frequency energy from said output waveguide.

6. Radio frequency apparatus according to claim 5, and further comprising a pair of opposed spaced shielding members associated with each said helices and each disposed about an end of a helix for affording effective radio frequency coupling of said helices to said waveguides.

References Cited by the Examiner FOREIGN PATENTS 2/1953 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

15 S. CHATMON, ]R., Assistant Examiner. 

1. A MULTIPLE BEAM KLYSTRON APPARATUS COMPRISING SPACED LONGITUDINALLY RESONANT INPUT AND OUTPUT WAVEGUIDES, INPUT MEANS FOR ESTABLISHING IN SAID INPUT WAVEGUIDE A STANDING ELECTROMAGNETIC WAVE AT A PREDETERMINED OPERATING FREQUENCY, EACH SAID WAVEGUIDES BEING PERIODICALLY LOADED BY A LONGITUDINALLY EXTENDING ARRAY OF RESONANT ELEMENTS EQUALLY SPACED APART ONE HALF OF A WAVEGUIDE WAVELENGTH AND SPACED FROM THE ENDS OF SAID SECTIONS ONE QUARTER OF A WAVEGUIDE WAVELENGTH AT SAID PREDETERMINED OPERATING FREQENCY, MEANS FOR PROJECTING A PLURALITY OF DISCRETE ELECTRON BEAMS TRANSVERSELY ACROSS SAID WAVEGUIDE IN SUCCESSION AND COINCIDENT WITH SAID RESONANT ELEMENTS FOR INTERACTION THEREWITH, MEANS DEFINING DRIFT SPACES BETWEEN SAID WAVEGUIDES FOR CONVERSION OF VELOCITY MODULATION OF SAID ELECTRON BEAMS TO DENSITY MODULATION, WHEREBY AN ELECTROMAGNETIC WAVE IS INTRODUCED IN SAID OUTPUT WAVEGUIDE CORRESPONDING IN FORM TO SAID WAVE IN SAID INPUT WAVEGUIDE, AND MEANS FOR EXTRACTING RADIO FREQUENCY ENERGY FROM SAID OUTPUT WAVEGUIDE. 